Hydrolysis of lactose and milk whey using a fixed‐bed reactor containing β‐galactosidase covalently bound onto chitosan and cross‐linked poly(vinyl alcohol)

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Abstract
Summary A fixed‐bed reactor containing β‐galactosidase from Aspergillus oryzae, immobilized onto either cross‐linked poly(vinyl alcohol) or natural polysaccharide chitosan, was used for the continuous hydrolysis of lactose and milk whey. Various conditions such as reactor temperature, substrate concentration, pH and flow rates were optimized for the effective operation of the reactor. The optimum pH and temperature for the immobilized system in the reactor was observed to be 5 and 50–60 oC, respectively. From the kinetic study the Michaelis constant (Km) and maximum reaction velocity (Vmax) for the free and immobilized system were calculated and were found to be 7.1 × 10−3 and 5.2 × 10−3 M, respectively, at 50 °C and pH 5 in citrate‐phosphate buffer. The energy of activation (ΔE), deactivation rate constant (Kd) and deactivation energy (ΔEd) were determined for the systems under study. Almost quantitative (∼95%) hydrolysis of lactose was achieved at the optimized conditions. The immobilized systems were observed to retain their activity even after 12–20 cycles.